U.S. Pat. Nos. 2,862,705, DDR (East Germany) DL-Pat. No. 43925 and BRD (Fed. Rep. Germany) DT-Pat. No. 2 241 127 describe apparatus for the mechanical threading of a paper web into the printing--drying--and cooling sections of rotary printing presses, by which the rapid, automatic insertion of the paper web into the starting position for the printing process is possible, with the danger of web tearing to a great extent eliminated.
In the arrangement of the U.S. Pat. No. 2,862,705 a pair of roller chains, one on each side of the paper web, running along the side of the provided path of insertion, are connected with an elastic cross ribbon to which the beginning of the web is attached. The system according to DDR Germany Patent comprises a roller chain with a latching clamp serving to grip the pointed end of the bias-cut paper web, on one side of the paper web only. In this design the relatively heavy pressure of the feed rollers prevents any deviation of the web from the straight path. The arrangement as per the DT-Patent employs also one roller-chain on the side only. This roller chain of a fixed length is being guided in a channel on the side of the printing press and is driven by a number of driving sheaves located at various points in this channel; by means of shunting switches located at different points in the channel insertion of the paper web can be accomplished at these points.
The printing press need not be altered to permit operation of these threading systems; they do not affect the set-up, thus permitting a speedy continuation of the printing process after a tearing of the web. They also result in a considerable reduction of the relatively high downtime required for the threading of a new web. However, they permit mechanized insertion of the web only up to the folding mechanism. Since the paper web is being folded lengthwise at the folding cone, or folding triangle, or former and due to the fact that the feed rollers downstream from the folding cone are perpendicular to the ones before this cone, it has up to now not been possible to devise a system for automatic threading into the folding mechanism. Rotary printing presses equipped with the above mentioned patented devices can be threaded into the folding mechanism only manually.
The beginning of the relatively wide paper web must be torn as square as possible (with respect to the edges of the web), and the web is then wrapped around the folding cone. To do this, the pressman has to place himself up on the frame of the machine, with his legs spread far apart. Thereafter he has to tap the two bottom feed rollers - one on each side of the wedge of the folding cone - with his hands to bring them into rotation and then to guide the paper web with both hands into the space between the two bottom feed rollers; in this manner the paper web which is being slowly transported by means of the folding roller ahead of the folding cone is gripped by the bottom feed rollers and can be transported to the next feed rollers. This operation is relatively time consuming; any benefit in the reduction in threading time--in itself arrived at only at considerable cost--is cancelled to a large extent. Also, the threading of the web is not always accomplished on the first try. But most of all, the manual threading can lead to serious accidents. Due to the limited accessibility to the folding cone the pressman's position is not secure; also he has to stretch far owing to the width of the paper web and he has to work fast since the machine is kept running continuously. Consequently it happens relatively frequently that he gets hurt when his fingers get caught between the two bottom feed rollers.